ALTIMETER DATA FOR OPERATIONAL USE IN THE MARINE ENVIRONMENT

Susan Digby, Thomas Antczak Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California Robert Leben, George Born, Suzanne Barth University of Colorado, Colorado Center for Astrodynamics Research, Boulder, Colorado Robert Cheney NOAA, Laboratory for Satellite Altimetry, Silver Spring, Maryland David Foley NOAA Coastwatch, and University of Hawaii, JIMAR, Honolulu, Hawaii Gustavo Jorge Goni NOAA Atlantic Oceanographic and Meteorological Laboratory, PhO, Miami, Florida Gregg Jacobs Naval Research Laboratory, Stennis Space Center, Mississippi Nick Shay University of Miami, Rosentiel School of Marine and Atmospheric Science, Miami, Florida

ABSTRACT an Earth orbiting satellite, have been used extensively by the science community to better TOPEX/Poseidon has been collecting altimeter understand ocean circulation and the role of the data continuously since October 1992. Altimeter oceans in climate and weather. As derived products data have been used to produce maps of sea surface have been made available, use of the data for height, geostrophic velocity, significant wave height, operational purposes has increased, as it has become and wind speed. This information is of proven use to evident that the data complements other information mariners as well as to the scientific community. Uses at the mariners disposal. It has also become apparent of the data include commercial and recreational that incorporation of altimeter data into weather and vessel routing, ocean acoustics, input to geographic climate forecasts increases the accuracy of these information systems developed for the fishing products. industry, identification of marine mammal habitats, II. PRODUCT TYPES fisheries management, and monitoring ocean debris. As with sea surface temperature data from the Product types include maps of sea surface height, Advanced Very High Resolution Radiometer (AVHRR) geostrophic velocity, significant wave height, and in the late 1980s and early 1990s, altimeter data wind speed. Products of most use to mariners are from TOPEX/Poseidon and ERS-1 and -2 are in the likely to be sea surface anomaly maps with process of being introduced to the marine world for superimposed geostrophic velocity vectors. operational maritime use. It is anticipated that over the next few years companies that specialize in A. Sea Surface Height producing custom products for shipping agencies, fisheries and yacht race competitors will be Sea surface height is defined as the distance of incorporating altimeter data into their products. The the sea surface above a known reference surface, data are also being incorporated into weather and such as the earth's ellipsoid or the marine geoid. The climate forecasts by operational agencies both in the sea surface height is computed from altimeter range US and Europe. This paper will discuss these and satellite altitude above the reference ellipsoid. products, their uses, operational demonstrations and (The "reference ellipsoid" is the first-order definition means of accessing the data. of the non-spherical shape of the Earth as an ellipsoid of revolution with equatorial radius of I. INTRODUCTION 6378.1363 kilometers and a flattening coefficient of 1/298.257.) An alternate reference surface to the Altimeter data products are in the process of earth's ellipsoid is the marine geoid, which is defined making the transition from scientific to operational as the shape the ocean would take if it were at rest. use. Altimeter data from TOPEX/Poseidon, which is When altimeter data are referenced to an ellipsoid the dominant pattern seen is the order 100 meter Current enters the Gulf between Yucatan and Cuba, amplitude signal of the marine geoid corresponding then loops and exits south of Florida through the to changes in sea surface height associated with Florida Straits. Circular streamlines depict the changes in the mass distribution of the earth. These locations of energetic anticyclonic (sea surface highs changes in height reflect changes in the gravity field shaded light gray) and cyclonic (sea surface lows and are useful for marine geology and offshore oil shaded dark gray) eddies that commonly occur in the and gas exploration. Of more interest to mariners is Gulf. The contour increment is 5 cm and every 10 the sea surface height relative to the geoid, which cm are annotated. This type of product is available shows the order one meter sea surface height on a daily basis from the University of Colorado. changes associated with the mean and time varying ocean circulation. Unfortunately, errors in current B. Geostrophic Velocity Vectors estimates of the marine geoid are large enough to prevent the accurate mapping of the mean Geostrophic velocity vectors are also a widely circulation at the smaller scales (<10 degrees) of used product and the vectors are most often provided interest to mariners. Fortunately, the time varying superimposed on maps of sea surface height or sea component can be measured accurately using an surface height anomalies. The geostrophic current is altimeter. For this reason sea surface height is often a major component of oceanic surface currents. shown as a sea surface height anomaly or deviation, Ocean currents are a function of wind forcing, tidal the difference between the sea surface height at the forces, buoyancy, and the Earth's rotation and time of measurement and the average sea surface gravity. The earth's gravity acts to move water from height for that region. Producers of these data use areas of higher water levels (pressure) to lower water various averages; some averages include all levels (pressure). When this component of the current available data and some averages are specific to caused by pressure is balanced with the component seasons. To recover the total sea surface height caused by the earth's rotations (Coriolis effect), the associated with the ocean circulation, a "synthetic" current is said to be geostrophic. In the deep ocean a observation is constructed by adding the mean large percentage of the ocean surface current is dynamic height determined from shipboard often in geostrophic balance and can be computed hydrographic measurements taken over the years to by knowing the changes in sea surface height and the anomaly. Maps derived by adding the sea surface the latitude of the point of interest. height anomaly to an estimated mean surface from hydrography realistically depict the total sea surface height associated with regions of persistent current such as the Gulf Stream in the North Atlantic and the Loop Current in the Gulf of Mexico.

Fig. 2. Estimated geostrophic flow field associated with the total sea surface height field depicted in Fig. 1. The flow field is visualized using streamlines determined from a 2-day integration of simulated particles released at grid points of the geostrophic velocity field. The magnitude of the geostrophic velocity is proportional to the sea surface slope and is Fig. 1. Synthetic total sea surface height field for the directed along isolines of constant height with higher Gulf of Mexico on February 11, 1999. This field was surface height values to the right (left) when facing in constructed by adding the mean sea surface height the direction of flow for the northern (southern) field from realistic numerical simulation of the Gulf hemisphere. Note the strong clockwise and to the interpolated altimeter measurements of counterclockwise circulation associated with the TOPEX/Poseidon and ERS-2 with respect to a long- anticyclonic and cyclonic eddies in the Gulf, term altimetric mean field. The streamlines (isolines respectively. This type of product is available on a of height) of the flow associated with the Loop daily basis from the University of Colorado. C. Wind Speed

Wind speed as measured from an altimeter is an indirect measurement based on the small-scale roughness of the sea surface. Wind speed is measured from the strength of the returned signal. There is a reliable relationship between the energy scattered from near-nadir and the wind speed. The altimeter does not give wind direction. Satellite scatterometer wind observations can used to determine both wind direction and magnitude and are of more use to the operational maritime community, however, wind speed from altimetry is useful for comparisons to these products. Altimetrically derived wind speeds are also valuable for generating wind climatologies because of the Fig. 3 Example of a chart provided to mariners by long time series available. private industry.

D. Significant Wave Height III. APPLICATIONS OF SPACEBORNE ALTIMETRY DATA Significant wave height is calculated from altimeter data based on the slope of the leading A. Ship Routing edge of the altimeter waveform, which is similar to a binned (time) histogram of the power returned by the Maps of sea surface anomalies overlaid with radar pulse after it bounces off the sea surface. A velocity vectors have been used in commercial calm sea with low waves returns a short, sharply shipping and competitive sailing to optimize the defined pulse whereas a rough sea with high waves route from one destination to another. The maps are returns a stretched pulse because the energy begins used to locate ocean features such as currents and to come back from the tops of the waves and eddies which are associated with high currents. In continues until the pulse hits the valley of the wave. cases where the rhumb line, the shortest distance The significant wave height is the average height of between two points goes though strong currents a the highest one-third of all waves in a particular time variety of tactics can be used. In the case where the period. Wave direction is not provided by altimeter rhumb line crosses orthogonal to a current, sailors are data. Maps of significant wave heights and wave likely to cross at a point and at an angle such that the height climatologies are useful for ship routing. duration of the crossing is minimized.

E. Combined Data Products Where the rhumb line crosses eddies, mariners use knowledge of the location of the eddies and velocity Combined data products are a final category of vectors to optimize their route. For instance, the information products. Products generated by the current speed in warm eddies, rotating clockwise University of Colorado and Stennis Space Center north of the Gulf Stream, averages 1-2 knots. Cold combine information from both TOPEX/Poseidon eddies circulate water in a counterclockwise and ERS-2 altimeters to better map the mesocale direction, south of the Gulf Stream, and average 2-3 circulation associated with eddies and meandering knots, and speeds of up to 7 knots have been currents. Private organizations have gone one step encountered. A sail boat must be on the correct side further in providing charts created by combining high of an eddy to take advantage of its current flow resolution information from complementary data sets direction. Also important is for ships to avoid such as sea surface temperatures and geostrophic situations in which the current flow direction is velocities. Examples of these companies are opposite to the wind direction. In this case, Scientific Fisheries Incorporated, Jenifer Clark’s dangerously high waves can form in locations such Gulfstream, and Roffer’s Ocean Fishing Forecasting as the Gulf Stream north wall. Service, Inc. Commercial companies provide charts to mariners that incorporate spaceborne altimeter data in support of races including the Bermuda Race which is one of the world's premiere sailing events. Hundreds of sailors gather to race the 635 mile course, starting from either Rhode Island or Massachusetts, and crossing the Gulf Stream to Bermuda. B. Ocean acoustics

Navy operations are critically dependent upon the ocean environment. Ocean acoustics determine the ability of ships to detect objects within the water, and the detection of objects such as submarines is vital to the safety of the fleet. Ocean acoustics in turn are determined by temperature and salinity properties within the ocean. Within the deep ocean, the dynamics affecting temperature and salinity may be measured through altimetry. Positive sea height anomalies (bulges) are usually associated with warm water and a depressed thermocline. Alternatively, sea level depressions are associated with cold water at a raised thermocline. One of the main sources of variability within the ocean is the mesoscale field, which is composed of eddies and current meanders. The mesoscale field is non-deterministic since the eddies and meanders are the product of instabilities and turbulence. Thus, it is not possible to predict the mesoscale field far in advance. Altimeter measurements provide one means for observing the mesoscale field and providing the ocean acoustic environment. One example of the effect of the mesoscale circulation on the ocean acoustic environment is given the Japan/East Sea just off the southeast coast of South Korea (Fig. 4). The acoustic signal excess provides an estimate of the acoustic signal of an object relative to the background noise level. If the acoustic signal excess is greater than zero then the reflected acoustic signal of an object is greater than the background noise, and the object is detected. Initially using a climatological density field based on the Generalized Digital Environmental Model (GDEM), the acoustic signal excess indicates a wide field of view. During this time, an intense AXBT survey provides the true synoptic environment. The true acoustic signal excess is significantly different from the field using the climatological environment and reveals a blind spot to the northeast of the acoustic receiver. The purpose of altimeter data is to provide a replacement for the large intensive AXBT survey. The Navy Modular Ocean Data Assimilation Fig. 4. The acoustic active signal excess calculated System (MODAS) uses historical in situ data to derive from climatological density field (top) and an in situ statistical relations between surface observations AXBT survey (bottom). The area is the Japan/East (dynamic height and temperature) and subsurface Sea off the east coast of Korea. Areas where the quantities (temperature and salinity). Based on the signal excess are greater than 0 indicate where derived surface to subsurface relations, given a underwater objects could be detected. The ocean measure of the surface height and surface density dramatically affects the sound propagation temperature it is possible to reconstruct the through the water, and the ocean mesoscale field subsurface temperature and salinity, (Fig. 5). The impacts the density structure. The difference statistical correlations vary spatially and seasonally as between the climatological result and the result with the vertical relations depend on the local in-situ sampling is due to ocean eddies. The environment and dominant oceanographic altimeter provides the ability to monitor the ocean processes. eddies and reconstruct the ocean acoustic field. cable laying and repair operations, a monitoring capability that is especially important when thermal imagery is not available because of cloud cover.

The offshore hydrocarbon industry has also made extensive use of near real-time altimeter products and an operational nowcast/forecast system relying on altimeter data assimilation (Kantha et al., 1999). In the Gulf of Mexico, from which nearly half of the US domestic oil is extracted, the strong currents (2 to 4 knots, 1-2 m/s) associated with the Loop Current and large Loop Current eddies impact hydrocarbon exploration and production activities along the Louisiana and Texas slope. An important aspect of the ocean monitoring and forecast system is the assimilation of near real-time altimeter data into a numerical ocean model of the Gulf of Mexico. For more than a year, near real-time nowcasts and forecasts have been made by the University of Colorado for potential use by the offshore oil and gas industry.

D. Debris Tracking:

Marine debris, floating and partially submerged material consisting of nets, timber, ship debris is increasing with human population and increasing contact with the sea. This material collects in locations based on wind and currents. Marine debris is capable of physically destroying coral, entangling marine mammals and can also be hazardous to small vessels. Russell E. Brainard, David G. Foley and R. Michael Laurs, of the NOAA/NESDIS CoastWatch Fig. 5. The temperature at 100 m is derived from the program, Hawaii Regional Node and the National sea surface height measured by altimeter satellites Marine Fisheries Service, Honolulu Laboratory are and the sea surface temperature. Warm core eddies investigating the potential of TOPEX/Poseidon and occur at 130E and 134E with a cold core eddy other remotely sensed data in identifying likely between the two. The water temperature affects the locations of marine debris. Complimentary remotely density and the propagation of sound through the sensed data sets are integrated to produce a tool that water. This is an example of a MODAS product can be used to study the SubTropical Convergence available from the Naval Research Laboratory at Zone (STCZ). The STCZ area is one of the primary Stennis. areas of responsibility for NMFS Honolulu Laboratory, and soon to be subject to much wider scrutiny due to C. Ocean Monitoring for Offshore Industries it's role in the transport and subsequent anchoring of Accurate estimates of the current and future state marine debris to the coral reefs of the Hawaiian of the ocean are very useful to industries involved in Archipelago. By its nature a convergent zone has offshore activities. Offshore operators that have used endemic cloud cover, complicating the use of altimeter-derived monitoring tools include sensors that require visible and infrared radiation companies working on ocean cable and hydrocarbon signals from the ocean surface. Thus a group are exploration and production activities. working to develop new products using data from microwave and radio frequency sensors which can Telecommunications is an important area of "see" through the clouds. Spaceborne altimeter data growth in the global economy. With the explosion of is one of these tools. These theories will soon be put world-wide communications, especially the Internet, to test in early 2000, when the Hawaii CoastWatch the need for underwater communication cables has satellite imaging team will use the remotely sensed increased dramatically. Cable laying and repair data sets to guide a Coast Guard vessel in the search requires accurate knowledge of the ocean circulation for debris in the open ocean. to minimize the impact of strong currents on the E. Fishing Industry: activities of the cable ship as it tends the cable and on underwater remotely operated vehicles working on Marine life is very often concentrated along the cable. The all-weather capability of altimeter oceanic frontal regions, which can be detected from data have been used to identify regions of strong altimeter-derived data. Operational tests of the utility currents along the edges of oceanic eddies near of products that incorporate altimeter data are in progress. In cooperation with NASA, satellite intensity changes of a given storm. The value of altimetry is being provided to SciFish to incorporate altimeter data is that heat content, which plays a role into their Geographical Information System (GIS), in the development and maintaining the formation of FishTrek98. The product runs on a laptop PC hurricanes, can be estimated from sea surface integrated with a Global Positioning System (GPS) topography. Research in both these areas is very receiver for real-time analysis and positioning. active in an effort to improve the predictions. FishTrek98 is designed to provide ship captains with a variety of essential information such as bathymetry, Currently, the National Hurricane Center provides snags, water temperature, historic catch figures, and seasonal forecasts, consisting of the number of name by catch. In addition, vessel captains can log their tropical storms per season. This is done using a catch, tide, current, marks, snags, temperature, sea variety of information, including the El Niño- conditions, weather, and lunar conditions in a Southern Oscillation (ENSO) status in the Pacific personalized electronic log book that is fully Ocean which is provided by the National Centers for integrated with all other available data sources. This Environmental Prediction (NCEP) from data sources product is currently in use by commercial fishermen, including the TOPEX/Poseidon altimeter and other and has received several favorable reviews. In remote sensing instruments. Once a hurricane is in January 1999, SciFish formed a focus group progress, its development is in part affected by the composed of fishermen from the various Bering Sea amount of heat in the upper ocean. An example of fisheries to evaluate FishTrek98 with satellite this was documented on October 4th, 1995, when altimeter, sea surface temperature, and sea ice real- Hurricane Opal deepened from 965 hPa to 916 hPa time data. Feedback from FishTrek98 users during the in the Gulf of Mexico over a 14 hour period after it 1999 fishing season will be used to access the utility encountered a warm core ring shed by the Loop of the data and improve the data products for future Current. As Hurricane Opal passed over one of the operational use. two warm rings existing at the moment in the Gulf of Mexico, the surface winds increased from 35 ms-1 to F. Fisheries Management more than 60 ms-1, and the radius of maximum wind decreased from 40 km to 25 km (Shay et al, in press). Fisheries management personnel also use Maps of upper ocean heat content are currently TOPEX/Poseidon data as one of a suite of tools to being produced in near-real time at NOAA/AOML understand the close relationship between the (http://www.aoml.noaa.gov/phod/cyclone/data/). marine environment and fishery dynamics. This type Further information on the relationship between sea of knowledge is essential to the management of height anomaly, upper layer thickness, sea surface sustainable fisheries. Other specific applications temperature and hurricane heat potential in the currently in development at the NMFS Honolulu western North Atlantic can be found on the web site Laboratory include satellite-derived tools to address listed above. the mitigation of fisheries interaction with sea turtles, the recovery of endangered Monk Seals and At the University of Colorado, the explosive growth monitoring and assessment of Coral reef ecosystems of Hurricane Opal has been accurately simulated by and essential fish habitats. Additionally, a recent a coupled atmosphere/ocean model by assimilating study funded by NOAA/NESDIS has focused on the altimeter data to define the conditions in the ocean impact of geostrophic currents on the recruitment of under the hurricane's path (Bao et al., in press). The spiny lobster larva. Spiny lobster larvae spend much success of such efforts highlight the future of their time in the region of the thermocline where operational uses of near real-time altimeter data for the current is largely geostrophically driven. Hence the accurate prediction of hurricane development geostrophic velocity vectors derived from TOPEX/Poseidon sea surface height data provide a As part of the United States Weather Research reasonable indication of the direction and speed that Program Hurricanes at Landfall, a joint NSF/NOAA the larvae will travel in their planktonic state. The experiment is being conducted over a warm core ring study, conducted for the Hawaiian Archipelago, in the Gulf of Mexico in the summer of '99. The shows that altimeter-derived geostrophic currents may experiment will deploy Airborne eXpendable Current be of use in predicting natural repopulation success. Profilers (AXCPs) and Airborne Xpendable Repopulation is a topic of growing interest as over Conductivity Temperature and Depth Profilers fishing occurs and efforts are made to replenish stock. (AXCTDs). These profilers will provide 3-dimensional This study by Jeffrey J. Polovina, Pierre Kleiber, and velocity and density data (temperature and salinity) Don Kobayashi of the National Marine Fisheries to compare to the fields derived from TOPEX Service Southwest Fisheries Science Center - altimeter. This research is supported by the National Honolulu Laboratory (see Polovina et al., 1999, Science Foundation and NOAA in support of the Fisheries Bulletin. 97:132-143). United States Weather Research Program on Hurricanes at Landfall. For more information see G. Hurricane Forecasting http://storm.rsmas.miami.edu/~nick and select wcr.html. Thus, by combining the early work of Altimeter data is one of the tools, along with other Leipper and Volgenau (1972) on hurricane heat remote sensing and in-situ data, used to both predict content with the two-layer model developed by Goni the severity of a hurricane season and to forecast et al. (1997) in combination with historical and in situ measurements (from aircraft), we will learn more H. Cetacean Habitat Monitoring about the role of the upper ocean on hurricane intensity change. Michelle Huber, a NOAA Altimeter data were used to locate eddies as part Forecaster Specialist at the National Hurricane of the 1996-1997 GulfCet program. GulfCet was a Center is working on transitioning the basic research field program run by Texas A&M oceanographers to operational forecasting of hurricane intensity based in College Station, marine mammal biologists changes. During this summer, we will build a data based in Galveston, with support from satellite base using both atmospheric and oceanic data in oceanographers at the University of Colorado. The these systems. goal of the program was to survey the abundance for the Gulf of Mexico’s 18 common cetaceans in continental margin areas of present oil and gas development. The survey also extended further offshore where oil and gas exploration will likely intensify in the near future. There is special interest in sperm whales because they are an endangered species.

Altimetric monitoring of the general circulation in the Gulf of Mexico served two purposes in GulfCet studies. Near-real-time altimeter data were used to map eddies, information which was used to plan research cruises to optimize the census process. Following the cruise historical altimeter data were used to map the fronts and eddies that occurred during the cruises. These historical data helped marine mammal biologists interpret when and where cetaceans were found during the cruises.

Scientists have learned that sperm whales are more abundant in cyclones and other habitats where nutrients and plankton are abundant near the surface. Where there were higher than average stocks of phytoplankton and squid, sperm whales gathered to feed. Locations of these cyclones can be tracked using altimeter data. Surveying these areas from ships enables scientists to gather information on numbers and behavior of cetaceans, (Ortega-Ortiz et al., 1999).

I. Forecasting of El Niño Related Climate Variations

El Niño-related climate variations often have widespread and devastating impacts. These include Fig. 6. Conditions in the Gulf of Mexico during the the frequency and severity of storms and the period September 18-28, 1995; before the passage of occurrence of droughts and floods. In the U.S. alone, hurricane Opal. business losses associated with 1986-87 El Niño a) TOPEX/Poseidon-derived sea surface height amounted to $10-15 billion. Although many of the anomaly field. consequences of El Niño cannot be prevented, b) Depth of the 20C isotherm (upper layer thickness) skillful forecasts enable resource managers in derived using the T/P sea height anomaly field and a climate-sensitive sectors to alter strategies and two-layer model. reduce economic vulnerability.’ (Cheney at al., c) TOPEX/Poseidon-derived upper ocean integrated 1998). NOAA (National Oceanic and Atmospheric vertical temperature (heat content) between the Administration) National Centers for Environmental surface and the depth of the 26C isotherm. The two Prediction (NCEP) has the mandate to provide warm rings in the Gulf of Mexico (WCR A and WCR B) forecasts to the nation to reduce loss of human life are characterized by their high sea height anomalies, and minimize economic impacts. large upper layer thickness and heat content values. The track of Hurricane Opal is superimposed on each Coupled ocean-atmosphere models have attained of the three panels. During October 4, 1995, significant forecast skill during the past decade, but hurricane Opal passed directly over WCR A, and they continue to be limited by an ocean observing increased its winds from 35 ms-1 to 60 ms-1. system which is extraordinarily modest. Satellites represent part of the solution. In particular, an operational flow of altimeter data has long been desired by the modeling community as a means of estimating changes in upper ocean heat (to first IV. DATA SOURCES: order, sea level is determined by the integrated temperature of the water column). But even though A. Near Real Time altimeters have flown nearly continuously since 1985, two challenges have stood in the way of Near real-time products from altimeter data are progress: (1) The altimeter data must be made made available by several organizations. The available fast enough (1-2 days) and with sufficient products vary in format, parameter, time interval accuracy (a few cm) to track changes in the ocean averaged and in time elapsed from data collection. within a tolerance that is useful for the ocean model; Products for marine operators are available from the (2) The assimilation method must be capable of Colorado Center for Astrodynamics Research, using a single parameter, sea level, to correct the University of Colorado, (http://www- model temperature as a function of depth. ccar.colorado.edu/~leben/research.html), the Naval Research Laboratory, Stennis Space Flight Center Using TOPEX/Poseidon altimeter data, both of (http://www7300.nrlssc.navy.mil/altimetry/), and the these problems have been solved through a Jet Propulsion Laboratory (JPL) Physical collaboration among NOAA, the Naval Oceanography Distributed Active Archive Center , Oceanographic Office (NAVOCEANO), and the Jet (PO.DAAC) (http://podaac.jpl.nasa.gov/topex). The Propulsion Laboratory (JPL). The program became National Oceanic and Atmospheric Administration operational in March 1997, just in time to assist in (NOAA) Laboratory for Satellite Altimetry also the long-range forecasts associated with the 1997- produces an operational near-real time sea level 1998 El Niño. The study by Cheney at al., showed product that predictions of Pacific sea surface temperatures, (http://ibis.grdl.noaa.gov/SAT/near_rt/topex_2day.ht a measure closely linked with El Niño/La Niña, that ml), that is assimilated into the operational NOAA were made with Topex ocean initial conditions have ENSO forecast models. In Europe, Developing Use of higher skill than those made with XBT (eXpendable Altimetry for Climate Studies (DUACS) also provides BathyThermographs) and the Tropical Atmosphere near-real time products (http://www.cls.fr/duacs). Ocean (TAO) data alone. Consequently, TOPEX data analyzed within 2 days of real time have been The MODAS system, at Stennis Space Fight added to the operational assimilation scheme Center presently uses real time altimeter data from implemented at NOAA NCEP. TOPEX/POSEIDON and ERS-2 to produce global sea surface dynamic height on a 1/8 degree grid. Sea surface temperature is also generated on a 1/8 degree grid based on real-time AVHRR data. The gridding of both the surface height and temperature is carried out in a manner to retain the local mesoscale variability and not to only produce the large-scale global dynamic height. The operations are performed globally to allow access to every region across the world. Using the gridded surface height and temperature, MODAS uses the statistical relations of surface to subsurface properties to generate the subsurface temperature and salinity.

The Quick Look Intermediate Geophysical Data Records (IGDRs) available from PO.DAAC is an 8 hour product automatically generated about an hour after downlink from the NASA Altimeter using the operational science software and a medium precision Global Positioning System (GPS) orbit. The products contain only the best quality data and data are provided in a simple ASCII format for ease of use. Parameters include sea surface height, sigma-0 and significant wave height. Derived parameters include wind speed, water vapor content and total electron content. Data are not available during Poseidon cycles. Fig. 7: The manifestation of the El Niño in sea surface height data is clearly visible in this image As mentioned in section II there are also a number that was obtained at the peak of the ‘97 - ‘98 El Niño. of private agencies producing ocean maps from data taken from a variety of sources. Many of these agencies also provide customized analysis for specific regions and support specific events. B. Climatologies of hurricane development”, Monthly Weather Review, 1999 (in press). Climatologies consist of averaged data usually over as many years as are available. Climatologies Cheney, R.E., L. Miller, C.K. Tai, J. Lillibridge, J. are valuable to the operations community for Kuhn, M. Ji, and D. Behringer, “Operational Altimeter planning, where a knowledge of what conditions to data processing and assimilation for El Niño expect is valuable. Many sites that provide near-real Forecasts”, AVISO Altimetry Newsletter, No. 6., April time data also provide archives and climatologies of 1998, p 36,37. these data. in addition, climatologies and historical altimeter data are available, at a higher precision Goni, G.J, S.L.Garzoli, A.J.Roubicek, D.B.Olson and than the near-real time data products, from the JPL O.B.Brown “Agulhas Ring Dynamics from PO.DAAC (http://podaac.jpl.nasa.gov/ TOPEX/POSEIDON Satellite Altimeter Data”, TOPEX_P.html) and from AVISO in France J.Mar.Res, 55, 861-883, 1997. (http://www-aviso.cls.cnes.fr/) Kantha, L.K., J.-K. Choi, R. R. Leben, C. Cooper, M. V. FUTURE DATA PRODUCTS AND DATA STREAMS Vogel and J. Feeney, “Hindcasts and Real-time Nowcast/Forecasts of Currents in the Gulf of Mexico”, To be truly operational, the stream of data must be Proceedings of the Offshore Technology Conference, assured. This is being accomplished with the Houston, TX, May 3-6, 1999. planned launch of Jason-1 in May 2000, a follow-on mission to TOPEX/Poseidon. In addition the ERS Leipper, D., and D. Volgenau, “Hurricane heat (European Remote Sensing) satellites also provide potential of the Gulf of Mexico”, J. Phys. Oceanogr., altimeter data. Altimeter data from these satellites 2, 218-224, 1972 are envisioned to contribute to the existing types of information products over the next decade. In Ortega-Ortiz, J. G., R. W. Davis, C. A. Ribic, D. C. addition it is anticipated that with growing familiarity Biggs, K. D. Mullin, R. R. Leben, W. E. Evans and B. of the benefits of altimeter data, that they will be Wursig, “Cetacean habitat associations in the used as a complement to other remotely sensed and northern Gulf of Mexico”, abstract, to be presented at in-situ data. It is anticipated that much of the the Society of Marine Mammalogy 13th Biennial generation of information products from remotely Conference, Maui, HW, Nov. 28 to Dec. 3, 1999. sensed data will occur in the private sector. Shay, L.K, G.J. Goni, and P.G. Black, “ Effects of a REFERENCES Warm Oceanic Feature on Hurricane Opal”, Monthly Weather Review, 1999 (in press). Bao, J.-W., J.M. Wilczak, J.-K Choi, and L. H. Kantha, ”Numerical Simulations of air-sea interactions under high wind conditions using a coupled model: A study